This application claims the benefit of Korean Application No. 33874/1997, filed Jul. 19, 1997, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
The present invention relates to a DVD (Digital Video Disc) player, and more particularly to a method for decoding video data at high speed, while maintaining synchronization between sub-picture data and MPEG (Motion Picture Experts Group) video data.
Multimedia information mainly comprises massive amounts of video data and audio data. When multimedia information is processed using PCM (Pulse Code Modulation), there may arise difficulty in recording and transmitting the massive amounts of data. Therefore, effective compression technologies for video and audio data will play a key role in realizing the multimedia era. It is expected that the real multimedia era will commence with the widespread adoption of the MPEG-2 standard and the AC-3 audio compression technique. The MPEG-2 standard is an international standard for compressing/multiplexing video and audio data. Particularly, MPEG-2 can reproduce images having a high resolution, as high as that in existing analog TVs, at a data transfer rate below 10 Mbps. For audio applications, the newly developed AC-3 audio compression technique can reproduce multi-channel audio data, so that one can enjoy high quality multi-channel sound at home.
At the present time, DVD recorders for recording compressed video and audio data and DVD players are rapidly becoming popular. A DVD player includes an A/V (Audio/Video) decoder for decoding compressed video and audio data. In known A/V decoders, when operating in a fast replay mode, sub-picture data is not synchronized with the MPEG video data. Thus, the sub-picture data and the MPEG video data are undesirably reproduced independently.
Accordingly, an object of the invention is to provide a method for decoding MPEG video data and sub-picture data in synchronism with each other in an A/V decoder when reproducing MPEG video data and sub-picture data in a fast replay mode.
According to an aspect of the present invention, there is provided a method for decoding video data in a decoder which reproduces MPEG video data and sub-picture data simultaneously at high speed. The method includes the steps of sequentially searching pictures to be reproduced, decoding the searched picture, and displaying the decoded picture, wherein a system clock reference (SCR) value is updated with a presentation time stamp (PTS) value of the decoded picture, the system clock reference being used for synchronizing a sub-picture decoding operation with an MPEG video data decoding operation; sequentially searching sub-picture units to be reproduced, analyzing a display control sequence (SP_DCSQ) in the searched sub-picture unit to compare command executing start time information (SP_DCSQ_STM) in said display control sequence (SP_DCSQ) with said updated system clock reference (SCR) value, and skipping the current display control sequence if the updated system clock reference value is greater than the command executing start time information, otherwise, executing all commands display control sequence such that the respective display control sequence is executed when the updated system clock reference value is equal to the command executing start time information.